For many years the market of the internal trim of motor vehicles has been dominated by the use of PVC sheets, either in combination with ABS for the dash-boards, or highly plasticized for the door trim and the manufacture of sun visors.
Although the properties of these materials are advantageous, there are nevertheless some disadvantages in employing PVC in this application. Besides those related to the use of plasticizer, such as fogging (evaporation of volatile constituents, in particular plasticizers, and their deposition on the window glasses) or embrittlement with time, PVC is not compatible with the majority of the other polymers employed in the motor vehicle industry, and this makes it necessary to separate it from other motor vehicle components before its possible recycling.
In the motor vehicle trim there is therefore a demand for a new material combining the good intrinsic properties of plasticized PVC (resistance to high and low temperatures, thermoformability, high-frequency weld-ability and flexibility) with the possibility of being easily recycled, especially by direct thermal recycling, or by reemploying it with other polymers employed in the motor vehicle.
The proposed compositions should not only provide the products resulting therefrom with excellent mechanical and stability properties, but should also be high-frequency weldable, with a view to being usable in the envisaged application. In addition, it is appropriate that the rheology of the compositions employed should be such as to permit thermoforming--and in particular graining--of high quality.
Various compositions based on polyolefins, in particular on a propylene homopolymer or copolymer, on ethylene-vinyl acetate copolymer and optionally on peroxide used as crosslinking agent during the conversion have already been proposed.
Thus, document U.S. Pat. No. 3,433,573 describes a mixture containing an olefin homopolymer and an ethylene-vinyl acetate copolymer, to which an organic peroxide may be added in an unspecified quantity before the mixing or during the latter (column 7, lines 48 to 60).
This mixture may be cured by means of an organic peroxide in a Banbury mixer, an extruder or a kneader, especially for forming sheets.
Document WO-93/24568 mentions compositions making it possible to obtain, especially by extrusion, products that can be high-frequency welded for various applications in the medical field, such as pouches, bags, tubes and closures.
The polymeric composition which is used contains at least one ethylene-vinyl acetate copolymer, at least one propylene homopolymer or copolymer, approximately 0.01% to 5% by weight of a crosslinking agent and approximately 0.1% to 35% by weight of one or a number of other polymers.